The present invention relates to an apparatus and method for separating and replacing a cap from a shank of a tip of a welding electrode.
It is known in the art that the electrode caps mounted on shanks of welding robots need to be periodically replaced by new ones because the caps are worn away due to their repeated use. Manually removing the caps is not possible because these are solidly wedged into their shank. Furthermore, the back surface of a cap is typically of only a few millimeters in thickness and therefore a very precise tool must be used.
Known in the art, there is U.S. Pat. No. 4,794,221 (TAKABE) which discloses an apparatus for removing electrode caps. The caps are removed by means of a tool that is inserted in the peripheral hollow joint that is defined between the shank and the cap. The tool is then pivoted downward against the back surface of the cap and the shoulder of the shank. One drawback of this known cap removing tool is that the shoulder of the shank may be damaged and the shank itself be deformed or unaligned as the cap is removed.
Also known in the art, there is U.S. Pat. No. 5,495,663 (SAITO) which discloses an apparatus for removing electrode caps designed to solve the problem of damage to shanks as identified above. The apparatus has two facing shank holders holding the shank from both sides. The apparatus also has electrode cap holders which are moved in a direction parallel to the axis of the shank to remove the cap from the shank by means of tapered sliding surfaces. One drawback of this known cap removing tool is that it requires the use of several components and it therefore does not provide an apparatus and method that can remove a cap from its shank in a simple and efficient manner.
An object of the present invention is therefore to provide an apparatus and method for separating a cap from a welding electrode by means of an apparatus that is simpler and more efficient than those provided in prior art.
According to the present invention, there is provided an apparatus for separating a cap from a shank of a tip of a welding electrode, said cap and said shank forming a peripheral hollow joint that is defined by a recessed end surface of the shank and a back surface of the cap, the apparatus comprising:
a guide frame having a recessed portion sized for receiving the tip of the welding electrode, said recessed portion extending in a direction perpendicular to said tip and having two facing side walls and an end wall, the side walls having guiding ribs that are inserted in the peripheral hollow joint for guiding the tip of the welding electrode into the recessed portion until the tip of the welding electrode is abutted against the end wall in an engaged position;
a cap withdrawing tool movably mounted on the guide frame, said cap withdrawing tool being movable along a crosswise direction that is perpendicular with respect to both the tip and the recessed portion when the tip of the welding electrode is in the engaged position, said tool having two facing wall sections each having a wedge that is inserted in the peripheral hollow joint when the tool is moved toward the tip of the electrode that is in the engaged position, said wedge being forced against the back surface of the cap for removing the cap from the shank when the tool is moved toward the tip of the electrode; and
a driving mechanism coupled to the cap withdrawing tool for moving the cap withdrawing tool toward and away from the tip of the welding electrode along the crosswise direction between an open position where the tip of the electrode is inserted into and removed from the recessed portion of the guide frame and a closed position where the wedge removes the cap from the shank.
According to another aspect of the present invention, there is also provided a method of separating and replacing first and second caps from first and second shanks of first and second tips of welding electrodes, said tips facing each other in a closable clamp arrangement and being held by opposite fingers pivotally mounted on an arm of a welding robot, said caps and said shanks forming first and second peripheral hollow joints that are defined by recessed end surfaces of the shanks and back surfaces of the caps, the method comprising the steps of:
a) inserting the first tip of the first welding electrode of the robot welder, in a first recessed portion of a first guide frame, said first recessed portion extending in a direction perpendicular to said first tip and having two first facing side walls provided with first guiding ribs and a first end wall;
b) guiding the first tip of the first electrode by means of the first guiding ribs of the first side walls that are inserted in the first peripheral hollow joint until the first tip of the first welding electrode is abutted against the first end wall in a first engaged position;
c) detecting that the first tip of the first welding electrode is in the engaged position;
d) moving a first cap withdrawing tool in a closed position, said first tool being mounted on the first guide frame along a first crosswise direction that is perpendicular with respect to both the first tip and the first recessed portion, said first tool having two facing wall sections each having a wedge being inserted in the first peripheral hollow joint and forced against the back surface of the first cap, thereby removing the first cap from the first shank;
e) moving said first cap withdrawing tool in an open position along the crosswise direction and simultaneously actuating an indexing mechanism that moves a first new cap mounted on a first holder of a cap supply drum in a home position;
f) positioning the first and second tips by means of the robot welder in the home position where the first tip is in alignment with the first new cap;
g) closing the first tip against the second tip to insert the first new cap into the first shank of the first tip;
h) inserting the second tip of the second welding electrode, by means of the robot welder, in a second recessed portion of a second guide frame, said second recessed portion extending in a direction perpendicular to said second tip and having two second facing side walls provided with second guiding ribs and a second end wall, said second guide frame being upside down with respect to the first guide frame;
i) guiding the second tip of the electrode by means of the second guiding ribs of the second side walls that are inserted in the second peripheral hollow joint until the second tip of the welding electrode is abutted against the second end wall in a second engaged position;
j) detecting that the second tip of the welding electrode is in the engaged position;
k) moving a second cap withdrawing tool in a closed position, said second tool being mounted on the second guide frame along a second crosswise direction that is perpendicular with respect to both the second tip and the second recessed portion, said second tool having two facing wall sections each having a wedge being inserted in the second peripheral hollow joint and forced against the back surface of the second cap, thereby removing the second cap from the second shank;
l) moving said second cap withdrawing tool in an open position along the crosswise direction and simultaneously actuating the indexing mechanism that moves a second new cap mounted on a second holder of the cap supply drum in the home position;
m) positioning the first and second tips by means of the robot welder in the home position where the second tip is in alignment with the second new cap; and
n) closing the second tip against the first tip to insert the second new cap into the second shank of the second tip.
The invention as well as its numerous advantages will be better understood by reading of the following non-restrictive description of a preferred embodiment made in reference to the appending drawings, in which like numerals refer to like elements.